ilvl may be too high now for some dungeons or raid, but I think we shouldnt search a solution in balancing that.
I would like to see dungeon achievements similar to other MMO, with the intend to deliberately make a boss mechanic harder to you and I would just make it require minimum ilvl but still be accessible by dutyfinder(so no premade required, could be done with a check in the duty finder option, similar to PvP freelancer). It creates replay value, a challenge for players who want more difficult 4man or 8man content without directly jumping into savage or ultimate. There could be specific titles and a mount for x number of dungeon achievements obtained as rewards. And boom you suddenly have content for weeks.
Idk why they already track dungeon completion time since ages, it has no use yet. Did they wanna create speed run competitive pve content similar to mythic dungeon in wow?